…er#169602)

Closes flutter#169598 (which explains
the integration test failure).
Closes flutter#169160.
Closes flutter#165803.

This is the only diff from 5d013c7:
```diff
diff --git a/packages/flutter_tools/lib/src/build_system/targets/common.dart b/packages/flutter_tools/lib/src/build_system/targets/common.dart
index 6158321..6773101 100644
--- a/packages/flutter_tools/lib/src/build_system/targets/common.dart
+++ b/packages/flutter_tools/lib/src/build_system/targets/common.dart
@@ -308,10 +308,18 @@ class KernelSnapshot extends Target {
     if (flavor == null) {
       return;
     }
-    if (!dartDefines.any((String element) => element.startsWith(kAppFlavor))) {
-      // If the flavor is not already in the dart defines, add it.
-      dartDefines.add('$kAppFlavor=$flavor');
-    }
+
+    // It is possible there is a flavor already in dartDefines, from another
+    // part of the build process, but this should take precedence as it happens
+    // last (xcodebuild execution).
+    //
+    // See flutter#169598.
+
+    // If the flavor is already in the dart defines, remove it.
+    dartDefines.removeWhere((String define) => define.startsWith(kAppFlavor));
+
+    // Then, add it to the end.
+    dartDefines.add('$kAppFlavor=$flavor');
   }
 }
 ```

…er#169602)

Closes flutter#169598 (which explains
the integration test failure).
Closes flutter#169160.
Closes flutter#165803.

This is the only diff from 5d013c7:
```diff
diff --git a/packages/flutter_tools/lib/src/build_system/targets/common.dart b/packages/flutter_tools/lib/src/build_system/targets/common.dart
index 6158321..6773101 100644
--- a/packages/flutter_tools/lib/src/build_system/targets/common.dart
+++ b/packages/flutter_tools/lib/src/build_system/targets/common.dart
@@ -308,10 +308,18 @@ class KernelSnapshot extends Target {
     if (flavor == null) {
       return;
     }
-    if (!dartDefines.any((String element) => element.startsWith(kAppFlavor))) {
-      // If the flavor is not already in the dart defines, add it.
-      dartDefines.add('$kAppFlavor=$flavor');
-    }
+
+    // It is possible there is a flavor already in dartDefines, from another
+    // part of the build process, but this should take precedence as it happens
+    // last (xcodebuild execution).
+    //
+    // See flutter#169598.
+
+    // If the flavor is already in the dart defines, remove it.
+    dartDefines.removeWhere((String define) => define.startsWith(kAppFlavor));
+
+    // Then, add it to the end.
+    dartDefines.add('$kAppFlavor=$flavor');
   }
 }
 ```

…ter/flutter#169602)

…ter/flutter#169602)

…169623)

This pull request is created by [automatic cherry pick workflow](https://github.com/flutter/flutter/blob/main/docs/releases/Flutter-Cherrypick-Process.md#automatically-creates-a-cherry-pick-request)
Please fill in the form below, and a flutter domain expert will evaluate this cherry pick request.

### Issue Link:
What is the link to the issue this cherry-pick is addressing?

#169602

### Changelog Description:
Explain this cherry pick in one line that is accessible to most Flutter developers. See [best practices](https://github.com/flutter/flutter/blob/main/docs/releases/Hotfix-Documentation-Best-Practices.md) for examples

Fixes a bug where `appFlavor` is `null` when being run with `flutter test` or being hot-restarted.

### Impact Description:
What is the impact (ex. visual jank on Samsung phones, app crash, cannot ship an iOS app)? Does it impact development (ex. flutter doctor crashes when Android Studio is installed), or the shipping production app (the app crashes on launch)

Cannot reliably use `appFlavor` without rebuilding the app from scratch.

### Workaround:
Is there a workaround for this issue?

Do not use hot restart, do not use `flutter test`.

### Risk:
What is the risk level of this cherry-pick?

### Test Coverage:
Are you confident that your fix is well-tested by automated tests?

### Validation Steps:
What are the steps to validate that this fix works?

Automated test coverage.

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